The present invention includes systems and method for making emergency calls. More specifically, the present invention includes routing an emergency call (e.g., an E911 call) through a public switched telephone network without sending the call through a dedicated emergency service (ES) trunk.
In the field of telephony, equipment and services for handling emergency telephone calls in the United States have been associated with the three-digit telephone number (TN) “9-1-1”. This system has gained widespread support and acceptance by telephone users over previous systems that normally required knowledge of the seven or ten-digit telephone numbers of public safety access points (PSAPs) (e.g., operators and dispatchers for police departments, fire departments, poison control centers, emergency medical services (EMS), hospitals, hazardous material recovery departments, etc.) that were in closest geographic proximity to the emergency situation. For a detailed legislative and technical history of the 9-1-1 system, please see U.S. Pat. No. 6,690,932, filed Sep. 11, 2000, and titled “System and Method for Providing Language Translation Services in a Telecommunications Network”, the entire contents of which are herein incorporated by this reference.
When systems and methods were first developed to handle emergency calls by dialing a three-digit emergency telephone number, network designers were concerned about managing such calls through existing public switch telephone networks (PSTNs). PSTNs at the time frequently experienced the so-called “Mother's Day Effect” when the number of telephone subscribers and users simultaneously using the network (e.g., people calling relatives on Mother's Day) exceeded network capacity and resulted in significant numbers of call failing to get completed.
Network designers and public safety officials agreed that emergency calls should not fail to be completed due to the Mother's Day Effect, and developed an more reliable (though more expensive) network infrastructure for emergency calls. This infrastructure (e.g., the 911 network infrastructure) had emergency calls (e.g., calls initiated by dialing 9-1-1) bypass the PSTN and to be placed directly on dedicated emergency service (ES) trunks that would send the calls to the appropriate emergency service router. The emergency service router would then route the calls to the appropriate PSAP. Typically, government regulations required that two or more redundant ES trunks be dedicated to each emergency service router so emergency calls would be assured of completion in the event of an ES trunk malfunctioning and/or failing. The system put in place did boost ease of use and reliability for completing emergency calls, but at a significant increase in infrastructure costs.
The burden of building and maintaining current 911 network infrastructure is relatively small in concentrated urban areas where costs are spread out over a large number of subscribers (e.g., metropolitan areas having more than 150,000 subscribers). However, in less densely and sparsely populated areas, the burden on individual subscribers to build and maintain this infrastructure is much larger, and often subsidized by state and federal fees on non-resident telephone subscribers. This fee revenue, however, may face significant reduction in light of the increased technological changes and cost competitiveness in the telecommunications industry. Thus, there remains a need to provide reliable emergency call service to all network users and subscribers at reduced costs.